The present invention relates, in general, to plastic injection molding arrangement and more particularly relates to an improved mold arrangements which facilitate changing of mold halves for successive molding operations and allows the use of molding equipment of substantially reduced size and weight because of the elimination of bulky mold bases required by prior art devices. It is well known in the prior art to use a pair of bases for carrying respective halves of a pair of injection mold inserts which are clamped together along a confronting face parting line to form an internal injection molding cavity in the mold inserts. Injection means are provided for supplying molten plastic material to the cavity to form a desired injection molded product.
Examples of such prior art arrangements are manufactured by Master Unit Die Products of Greenville, Michigan and generally idenified as "MUD" frames and unit die inserts. These frames and inserts are designed to be used in matching pairs where the large frames each have a recess arranged to accommodate corresponding die or mold inserts. The confronting faces of the frames of the die or mold inserts determine the parting line of the molded product. The prior art taught that in order to maintain dimensional stability the frames had to be of heavy construction, generally steel, and in order to change from one die size to another die size the frame from the first die had to be removed from the machine and replaced with a frame for the second die insert. The frames were heavy and were bolted to the injection molding machine. Also where a coolant was utilized, the coolant source was connected to the frames and had to be disconnected when the frame was removed, thereby further complicating the operation and leading to increased labor cost. Further the frequent connection and disconnection of the coolant lines promoted leaks in the system.
U.S. Pat. Nos. 4,158,910 and 4,202,522 teach arrangements which can be used on several die inserts. However even the devices taught by these references are large and cumbersome. Changeover may occur daily or even more than once a day and the time spent in such changeover is a significant part of the cost of producing molded products. The arrangement shown in the references and the devices provided by Master Unit Die Products equally consume operator time in changeover.
Moreover, devices shown in the a forenoted references, and the Master Unit Die configurations, require heavy blocks to be moved in order to position the dies; whereas in order to facilitate operation of an injection molding operation it is desirable to minimize the forces required and the weight of the blocks which must be moved. Equally desirable is a means for quickly inserting and removing mold parts so that changeover from one operation to another is further facilitated and the time required for changover reduced.
An additional feature of the present invention is the recognition that in most prior art devices the base is first attached to the injection molding machine and then the mold is secured in the base. Inherent in such arrangements is the massive size of the devices which require larger framemachines to hold the devices and the attendant additional cost and labor.
Furthermore, prior art devices, including devices in accordance with the aforenoted references, require a relatively large barrel injection device which holds more material than necessary in devices in accordance with the present invention and since the material tends to degrade during storage there is an excessive loss of material due to degradation in the prior art devices.
Other arrangements relating to die assemblies are shown in U.S. Pat. No. 3,103,705; U.S. Pat. No. 2,447,101; U.S. Pat. No. 4,330,248;
No prior art arrangement is known which provides the advantages features set out applicants invention as disclosed hereinafter.